1. Field of the Invention
The present invention generally relates to input devices, and more particularly to an input device for inputting information into an electronic system including but not limited to a portable wireless terminal. The present invention is also a method for a keypad of this type.
2. Background of the Related Art
Communication terminals generally include telephones commonly used in the home or office and portable wireless terminals. Portable wireless terminals have developed more functions as wireless communication techniques have evolved. These functions include voice transmission/reception, letter message transmission, data transmission, and image transmission/reception.
A keypad used as a switching device for generating input signals and setting various functions is used not only in general telephones but also in portable wireless terminals. Keypads of this type have keys on which numbers and letters are printed, and the keys are assembled in a front housing of the terminal in an operative state. The keypad is used to perform various functions, and is externally exposed thereby making its design, preference pattern, visual effect, and endurance very important.
FIG. 1 shows disassembled view of a portable wireless terminal. This terminal includes a folder 2 coupled to one side of a front case 1 by a hinge 3. A rear case 4 is also coupled to the front case. A printed circuit board 5 has contact points 5a arranged at an inner space formed between the front and rear cases. A dome switch assembly 6 is located adjacent the printed circuit board and a keypad made of a hard material is arranged on the dome switch assembly. The keypad is formed of a thin-film sheet 11 and keys 12 are formed on an upper surface of the sheet. The keys are inserted into respective holes 1a in the front case in such a manner that a part of each key is exposed to an outer portion of the terminal through the holes 1a. 
FIG. 2 shows an isolated view of a related-art keypad which may be inserted into the portable wireless terminal shown in FIG. 1, and FIG. 3 is a sectional view taken along line A-A of FIG. 2. In the keypad, a dome switch 6 having an elastic force and a restoration force is mounted on the printed board 5, and keypad 10 having a key 12 formed on one part of sheet 11 is located adjacent the dome switch. A soft silicon material 13 is molded into the key.
The aforementioned keypad of the related art has a number of drawbacks. One drawback relates to the material from which keys of the keypad are made. As shown in FIGS. 2 and 3, each key of the keypad is made of a hard material, which makes its forming operation difficult and makes it difficult to change the key into various designs. That is, since a film of hard material is used to form each key, shapes of the keys are limited. For example, an edge part of each key is smashed which gives the key an ambiguous appearance. Also, since it is difficult to form a decoration line for beauty at the key surface, the appearance of the key is not beautiful.
FIG. 4 shows another related-art keypad for a portable wireless terminal, and FIG. 5 is a sectional view taken along line B-B of FIG. 4. In these figures, dome switch 6 is mounted on a printed circuit board 5 and a supporting member 23 of silicon material and having a protrusion 23a is located on the dome switch. A keypad 20 is installed on an upper surface of the supporting member, and a plurality of keys 22 of plastic material are attached to predetermined positions on an upper surface of a pad sheet 21 of the keypad using an adhesive (not shown).
The aforementioned related-art keypad also has a number of drawbacks. For example, when appearance is processed by spray painting and ultraviolet coating, the painting and coating are applied to an adhesion part of the keys. As a result, the keys do not adhere to the keypad completely but are shaken, or an adhesion position of the keys becomes deteriorated or distorted. Also, since heights of the keys are different from one another based on the amount of adhesive applied to fix each key to the pad sheet, each key has a different feeling or touch which thereby degrades reliability of the product. Also, since the keys are not in precise alignment with the key holes in the front case, quality of appearance is deteriorated and the user has a degraded pressing feeling for the keys.